Well sealing method for forming barrier by using rock salt creep in salt cavern carbon sequestration well

Abstract

The invention discloses a well shut-in method for forming a barrier in a salt cavern carbon sequestration well through rock salt creep. The well shut-in method comprises the following steps that S1, a target salt cavern carbon sequestration well is selected; s2, a bottom bridge plug is put into the bottom of the shaft; s3, a sleeve forging and milling tool is put into the salt rock layer section, the sleeve above the bottom bridge plug is cut off, and an annular cement sheath of the salt rock layer section is removed to form a reaming section; s4, the drilling fluid is circulated to remove casing pipe and cement sheath scraps in the shaft; s5, the diameter of the reaming section is measured; s6, backfilling broken salt rock to the reaming section, and compacting to form a broken salt rock backfilling section; s7, a top bridge plug is put into the upper portion of the broken salt rock backfill section so as to pack the broken salt rock backfill section; and S8, a cement well plugging material is injected above the top bridge plug, and a cement plug is formed. According to the method, the backfill well section can be repaired by utilizing the creep behavior of the rock salt of the broken rock salt backfill section under the high-temperature and high-pressure conditions, the original porosity and permeability of the cover layer are recovered, and the natural salt barrier is re-established.

Description

Technical Field

[0001] The present invention relates to the technical field of wellbore sealing, and particularly to a well sealing method for forming a barrier by using salt rock creep in a salt cavern carbon sequestration well. Background Art

[0002] Rock salt in China is buried underground at a depth of tens of meters to about 5,000 meters, and the thickness ranges from dozens of meters to hundreds of meters. After long-term solution mining, rich salt cavern resources have been formed. Salt caverns are ideal carbon storage sites due to their low permeability, stable chemical properties, and non-reaction with carbon dioxide. Salt cavern carbon sequestration is a technology that uses a wellbore to transport liquefied carbon dioxide to an underground salt cavern for permanent storage. Due to the long storage time, there is a risk of carbon dioxide leakage along the wellbore. Therefore, a well sealing method for maintaining long-term wellbore sealing is crucial.

[0003] For the permanent storage of carbon dioxide, the conventional well sealing method is the injection plugging method, that is, squeezing a plugging material (usually cement) into the target well section to make it enter the formation, the damaged part of the casing, or the annulus outside the casing to form a plug, and controlling the plug in the well at the designed position. Due to the extremely strong creep ability of salt rock, continuous extrusion of the wellbore will cause wellbore damage and lead to seal failure problems. In addition, if the salt cavern contains water, carbon dioxide will dissolve in water to produce an acidic environment, continuously corroding the casing and the cement sheath, and there is a risk of leakage. The carbon dioxide leakage caused by wellbore seal failure severely restricts the large-scale development of salt cavern carbon sequestration. Therefore, when storing carbon dioxide in a salt cavern, how to achieve permanent wellbore sealing is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0004] Aiming at the above problems, the present invention aims to provide a well sealing method for forming a barrier by using salt rock creep in a salt cavern carbon sequestration well.

[0005] The technical solution of the present invention is as follows:

[0006] A well sealing method for forming a barrier by using salt rock creep in a salt cavern carbon sequestration well, comprising the following steps:

[0007] S1: Select a wellbore suitable for forming a barrier by using salt rock creep as the target salt cavern carbon sequestration well, and obtain the initial moisture content of the salt rock from the core library collected during drilling;

[0008] S2: Lower a bottom bridge plug into the bottom of the wellbore to isolate the carbon dioxide already injected in the salt cavern;

[0009] S3: Lower a casing milling tool to the salt rock formation section, cut off the casing above the bottom bridge plug, and remove the cement sheath in the annulus of this salt rock formation section to form an enlarged hole section;

[0010] S4: Circulate the drilling fluid to remove the debris of the casing and cement sheath in the wellbore, then displace the drilling fluid in the wellbore with a large amount of clear water, and finally displace the fluid in the wellbore with gas;

[0011] S5: Lower a wellbore diameter measuring tool to measure the diameter of the reamed section;

[0012] S6: Lower a coiled tubing with a bottom drain port into the well. According to the measurement result of the diameter of the reamed section, backfill the reamed section with crushed salt rock from the annulus outside the coiled tubing. After backfilling is in place, supplement water to the crushed salt rock through the drain port of the coiled tubing; the salt rock in the crushed salt rock backfill section undergoes creep under the formation high temperature and high pressure conditions, and the creep rate increases after water supplementation, forming a natural salt barrier;

[0013] S7: Lower a top bridge plug above the crushed salt rock backfill section to seal off the crushed salt rock backfill section;

[0014] S8: Inject cement well sealing material above the top bridge plug to form a cement plug.

[0015] Preferably, in step S1, the wellbore suitable for forming a barrier by salt rock creep refers to a wellbore where the thickness of the salt cavern top is not less than 80 m.

[0016] Preferably, in step S2, the bottom bridge plug is installed at a wellbore position at least 30 m above the bottom of the well.

[0017] Preferably, in step S3, the height of the reamed section is greater than 50 m.

[0018] Preferably, in step S4, weighted drilling fluid is used to remove the debris of the casing and cement sheath in the wellbore.

[0019] Preferably, in step S6, the volume of the backfilled crushed salt rock is calculated by the following formula:

[0020]

[0021] In the formula: V is the volume of the backfilled crushed salt rock, m 3 ; n is the number of sections of the reamed section; r i is the wellbore radius of the i-th section of the reamed section, m; h i is the wellbore height of the i-th section of the reamed section, m;

[0022] The volume of water supplemented to the crushed salt rock is calculated by the following formula:

[0023]

[0024] In the formula: W is the volume of water supplementation, m 3 ; W n is the moisture content of the salt rock recorded during drilling coring, %; Wo Moisture content of the backfilled crushed salt rock measured on site, %.

[0025] Preferably, in step S8, the cement well plugging material is injected by the circulating plugging method.

[0026] Preferably, in step S8, the height of the cement plug is greater than 30 m.

[0027] Preferably, it further includes the step of setting a carbon dioxide monitor at the wellhead to monitor whether there is carbon dioxide leakage from the wellbore.

[0028] Preferably, the monitoring interval of the carbon dioxide monitor is not less than once every 12 hours.

[0029] The beneficial effects of the present invention are as follows:

[0030] (1) In the present invention, the crushed salt rock is backfilled to the bottom of the well, and the creep behavior of the original salt rock formation under high temperature and high pressure is utilized to continuously extrude the backfilled crushed salt rock, reducing the porosity and permeability of the backfilled section until it is consistent with the original salt rock formation, and re-establishing a natural salt barrier.

[0031] (2) The natural salt barrier formed by the creep of salt rock in the present invention not only ensures the permanent storage of carbon dioxide, but also avoids the problem of carbon dioxide corrosion, and solves the problem of carbon dioxide leakage along the wellbore. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 It is a schematic flow chart of the well plugging method for forming a barrier by using salt rock creep in the salt cavern carbon sequestration well of the present invention.

[0034] Reference numerals in the figure: 1 - casing; 2 - cement sheath; 3 - salt rock formation; 4 - bottom bridge plug; 5 - reaming section; 6 - crushed salt rock; 7 - top bridge plug; 8 - cement plug; 9 - carbon dioxide monitor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, without conflict, the embodiments in the present application and the technical features in the embodiments may be combined with each other. It should be pointed out that unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs. The terms such as "including" or "comprising" used in the disclosure of the present invention mean that the elements or objects appearing before the term cover the elements or objects listed after the term and their equivalents, without excluding other elements or objects.

[0036] As Figure 1 shown, the present invention provides a well sealing method for forming a barrier by utilizing the creep of salt rock in a salt cavern carbon sequestration well, including the following steps:

[0037] S1: Select a wellbore suitable for forming a barrier by utilizing the creep of salt rock as the target salt cavern carbon sequestration well, and obtain the initial moisture content of the salt rock from the core library collected during drilling.

[0038] In a specific embodiment, the wellbore suitable for forming a barrier by utilizing the creep of salt rock refers to a wellbore with a salt cavern top thickness of not less than 80 m.

[0039] S2: Lower a bottom bridge plug 4 to the bottom of the wellbore 1 to seal off the carbon dioxide already injected into the salt cavern.

[0040] In a specific embodiment, the bottom bridge plug 4 is installed at a wellbore position at least 30 m above the bottom of the well.

[0041] S3: Lower a casing milling tool to the salt rock formation section 3, cut off the casing 1 above the bottom bridge plug 4, and remove the annulus cement sheath in this salt rock formation section to form an enlarged hole section 5.

[0042] In a specific embodiment, the height of the enlarged hole section 5 is greater than 50 m.

[0043] S4: Circulate the drilling fluid to remove the casing and cement sheath debris in the wellbore, then replace the drilling fluid in the wellbore with a large amount of clear water, and finally replace the fluid in the wellbore with gas.

[0044] In a specific embodiment, a weighted drilling fluid is used to remove the casing and cement sheath debris in the wellbore. Optionally, the weighted drilling fluid is composed of barite and bentonite. In this embodiment, using a weighted drilling fluid to remove the casing and cement sheath debris in the wellbore can inhibit the creep process of the surrounding exposed salt rock formation during the reaming operation.

[0045] S5: Lower a well diameter measuring tool to measure the diameter of the enlarged hole section 5.

[0046] In a specific embodiment, the well diameter measuring tool is lowered by means of wireline logging.

[0047] S6: Run a coiled tubing with a bottom drain hole into the well. According to the diameter measurement result of the reamed section 5, backfill the reamed section 5 with crushed salt rock 6 from the annulus outside the tubing. After backfilling is completed, supplement water to the crushed salt rock through the drain hole of the coiled tubing; the salt rock in the backfilled section of the crushed salt rock undergoes creep under the formation high temperature and high pressure conditions, and the creep rate increases after water supplementation, forming a natural salt barrier.

[0048] In a specific embodiment, the volume of the backfilled crushed salt rock is calculated by the following formula:

[0049]

[0050] where: V is the volume of the backfilled crushed salt rock, m 3 ; n is the number of sections of the reamed section; r i is the wellbore radius of the i-th section of the reamed section, m; h i is the wellbore height of the i-th section of the reamed section, m;

[0051] The volume of water supplemented to the crushed salt rock is calculated by the following formula:

[0052]

[0053] where: W is the volume of water supplementation, m 3 ; W n is the moisture content of the salt rock recorded during drilling core sampling, %; W o is the moisture content of the backfilled crushed salt rock measured on site, %.

[0054] In a specific embodiment, the crushed salt rock is the salt rock that is returned to the ground and collected and stored during drilling.

[0055] S7: Run a top bridge plug 7 into the well above the backfilled section of the crushed salt rock to seal off the backfilled section of the crushed salt rock.

[0056] S8: Inject cement well sealing material above the top bridge plug 7 to form a cement plug 8.

[0057] In a specific embodiment, the cement well sealing material is injected using the circulating plugging method, and the height of the cement plug 8 is greater than 30 m.

[0058] In a specific embodiment, the well sealing method for forming a barrier by using salt rock creep in the salt cavern carbon sequestration well of the present invention further includes a step of setting a carbon dioxide monitor 9 at the wellhead to monitor whether there is carbon dioxide leakage from the wellbore. Optionally, the monitoring interval of the carbon dioxide monitor 9 is not less than once every 12 hours.

[0059] In a specific embodiment, taking a 3000-meter well as an example, the well sealing method using salt rock creep to form a barrier in the salt cavern carbon sequestration well of the present invention is adopted. After about 1 year, the crushed salt rock backfilled can return to the original stress state and at the same time restore to the original salt rock permeability. The backfilled well section is repaired, and a natural salt barrier is re-established.

[0060] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the above-disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier, characterized in that: The following steps are involved: S1: Select a wellbore suitable for using salt rock creep to form a barrier as the target salt cavern carbon fixation well, and obtain the initial water content of the salt rock from the core library collected during drilling; S2: insert a bottom bridge plug at the bottom of the wellbore to isolate the injected carbon dioxide in the salt cavern; S3: Run the casing forging and milling tool into the salt rock section, cut off the casing above the bottom bridge plug, and remove the cement ring in the annulus of the salt rock section to form an expanded hole section; S4: Circulate drilling fluid to remove casing and cement sheath debris in the wellbore, then replace the drilling fluid in the wellbore with a large amount of clean water, and finally replace the fluid in the wellbore with gas; S5: running a wellbore diameter measuring tool to measure the diameter of the reaming section; S6: a coiled tubing with a bottom drainage port is lowered into the well, and according to the diameter measurement result of the reaming section, broken salt rock is backfilled from the annulus outside the tubing to the reaming section, and water is added to the broken salt rock through the drainage port of the coiled tubing after the backfilling is in place; the salt rock in the broken salt rock backfill section creeps under the high temperature and high pressure conditions of the formation, and the creep speed is increased after the water is added, so as to form a natural salt barrier; S7: lowering a top bridge plug above the crushed salt rock backfill section to isolate the crushed salt rock backfill section; S8: injecting cement well sealing material above the top bridge plug to form a cement plug.

2. The method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier according to claim 1, characterized in that: In step S1, the wellbore suitable for utilizing salt rock creep to form a barrier refers to a wellbore that satisfies the requirement that the thickness of the top of the salt cavern is not less than 80 m.

3. The method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier according to claim 1, characterized in that: In step S2, the bottom bridge plug is installed at a wellbore position at least 30 m above the well bottom.

4. The method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier according to claim 1, characterized in that: In step S3, the height of the reaming section is greater than 50m.

5. The method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier according to claim 1, characterized in that: In step S4, the casing and cement sheath debris in the wellbore are removed using a weighted drilling fluid.

6. The method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier according to claim 1, characterized in that: In step S6, the volume of the backfilled crushed salt rock is calculated by the following formula: Where: V is the volume of the backfilled broken salt rock, m 3 ; n is the number of eye-enlarging sections; r i is the wellbore radius of the i-th section of the expansion section, m; h i is the wellbore height of the i-th section of the expansion section, m; The volume of water added to the crushed salt rock is calculated by the following formula: Where: W is the water replenishment volume, m 3 ; W n is the water content of salt rock recorded during core drilling, %; W o is the moisture content of backfill crushed salt rock measured on site, %.

7. The method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier according to claim 1, characterized in that: In step S8, the cement well sealing material is injected using a cyclic plugging method.

8. The method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier according to claim 1, characterized in that: In step S8, the height of the cement plug is greater than 30m.

9. The method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier according to any one of claims 1 to 8, characterized in that: The method also includes the step of setting a carbon dioxide monitor at the wellhead to monitor whether there is carbon dioxide leakage from the wellbore.

10. The method for sealing a well in a salt cavern carbon fixation well by using salt rock creep to form a barrier according to claim 9, characterized in that: The monitoring interval of the carbon dioxide monitor shall not be less than once every 12 hours.

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